Novel, Moon and Mars, partial gravity simulation paradigms and their effects on the balance between cell growth and cell proliferation during early plant development

11 p.-8 fig.-1 tab.Clinostats and Random Positioning Machine (RPM) are used to simulate microgravity, but, for space exploration, we need to know the response of living systems to fractional levels of gravity (partial gravity) as they exist on Moon and Mars. We have developed and compared two different paradigms to simulate partial gravity using the RPM, one by implementing a centrifuge on the RPM(RPMHW), the other by applying specific software protocols to driving the RPM motors (RPMSW). The effects of the simulated partialgravity were tested in plant root meristematic cells, a system with known response to real and simulated microgravity. Seeds of Arabidopsis thaliana were germinated under simulated Moon (0.17 g) and Mars (0.38 g) gravity. In parallel, seeds germinated under simulated microgravity (RPM), or at 1 g control conditions. Fixed root meristematic cells from 4-day grown seedlings were analyzed for cell proliferation rate and rate of ribosome biogenesis using morphometrical methods and molecular markers of the regulation of cell cycle and nucleolar activity. Cell proliferation appeared increased and cell growth was depleted under Moon gravity,compared with the 1g control. The effects were even higher at the Moon level than at simulated microgravity, indicating that meristematic competence (balance between cell growth and proliferation) is also affected at this gravity level. However, the results at the simulated Mars level were close to the 1g static control. This suggests that the threshold for sensing and responding to gravity alteration in the root would be at a level intermediate between Moon and Mars gravity. Both partial g simulation strategies seem valid and show similar results at Moon g levels, but further research is needed, in space flight and simulation facilities,especially around and beyond Mars g levels to better understand more precisely the differences and constrains in the use of these facilities for the space biology community.Funding: for [JvL]: Grant ALW-GO-MG/10-07 from the Netherlands Organization for Scientific (NWO) Research Earth and Life Sciences (ALW)via the Netherlands Space Office (NSO) and the ESA contract 4000107455/12/NL/PA.For [FJM]: Grant ESP2015-64323-R from the Spanish National Plan for Research and Development (MINECO-ERDF co-funding). For [RH]: ESA-ELIPS Program ESA GIA Project, contract number 4000105761. [AM] was recipient of a fellowship of the Spanish National Program for Young Researchers Training (MINECO, Ref. BES-2013- 063933).Peer reviewe

Differential responses to salt stress in ion dynamics, growth and seed yield of European quinoa varieties

Quinoa is a nutritious seed crop with a great potential to grow in saline soils. Here, we studied ion concentrations in quinoa tissues throughout the life cycle of the plant, and linked ion dynamics to responses in growth parameters, seed yield and efficiency of photosynthesis under salinity (0–400 mM NaCl). Ion dynamics changed from high ion exclusion (>99 %, root contents lower than root medium and low accumulation of ions in the leaves) before flowering, to a build-up of ions during seed filling. This indicates a change in strategy in maintaining the necessary gradient of water potential from the root medium to the leaves. K+ concentrations in leaves also increased by more than 100 % in response to prolonged severe salt stress, which may point to a role of this ion in leaf osmotic adjustment. Accumulation of ions in epidermal bladder cells did not contribute substantially to Na+-exclusion as it was less than 6 % of the total Na+ taken up in leaves. Growth under salt stress was mostly impaired by anatomical adaptations (reduced SLA), while initial light use efficiency (Fv/Fm) and NAR were not affected. The variety Pasto showed a “survival strategy” to high salinity with higher ion exclusion and a higher reduction in transpiration than the other varieties, at the expense of lower biomass and seed yield.</p